Thank, hotkee. I had not done that, and I got a successful upgrade message, and even saw my sidebar and links and things show up, but no main post section. I’m confident it’s all there, of course, and it was high time I updated my theme anyway (thanks for the comment, iridiax), so I don’t mind losing that.
Now I just need to figure out the last couple of steps. In the time when I thought I’d lost everything, I removed the index.php file and replaced it with a short custom message on an index.html file. My wordpress files are in a subfolder below my domain root; what 2.5.1 files need to be at the root? I think it’s index.php and missing.php?
I’m gonna try and check the documentation, but I’ll check back here as well. Thanks again.